| Summary: | 碩士 === 國立彰化師範大學 === 生物學系 === 96 === Abstract
Most aphids carry the endosymbiont Buchnera aphidicola. Aphids obtain nutrients from plant sap, which contains few essential nitrogen compounds, such as tryptophan. These compounds were offered by B. aphidicola. The tryptophan synthesis pathway converts chorismate into tryptophan through a series of chemical reactions, and is feedback inhibited by tryptophan on the first enzyme anthranilate synthase. This enzyme is a heterotetramer encoded by trpE and trpG genes. Compared with E. coli, B. aphidicola genome does not possess the regulatory gene trpR. Therefore I decided to study the feedback-inhibition property of anthranilate synthase from Buchnera. By measuring the inhibition of tryptophan analogs on the growth of E. coli trpE mutant complemented by Buchnera trpE, I discovered that the B. aphidicola enzyme is more sensitive to the inhibitors IAA (3-indoleacrylic acid) and α-MT (α-Methyltryptophan) than the E. coli enzyme. By inducing trpEG expression with IPTG (isopropyl-beta-D-thiogalactopyranoside), I demonstrated that these genes were the targets of IAA and alpha-MT. Furthermore, both compounds suppressed the growth of aphids in in vivo experiments using a birdcage device and artificial diets. I measured the change in body weight and survival of aphids fed with IAA or a-MT-containing diet for one week. Compared to the control group, the survival of inhibitor-fed groups droped in a dosage-dependent manner., but there is no significant difference in the body weight between the control and inhibitor-fed groups.
關鍵詞：Escherichia coli: E. coli，AS: anthranilate synthase，TRP: tryptophan，Bu-AS: Buchnera-Anthranilate synthase。
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